Overclocking is a sort of rite of passage for PC enthusiasts. You're not truly hardcore until you've pushed your hardware beyond the stock speeds defined by the manufacturer. Back in the day, that meant fiddling with DIP switches, navigating arcane BIOS interfaces, and sometimes even making hardware modifications with a #2 pencil. Also, we had to walk barefoot through several feet of snow just to get our hands on the hardware; Newegg wasn't around, and Amazon only sold books.
Today, clock boosting couldn't be easier. AMD and Intel both offer CPUs with fully unlocked multipliers, the holy grail of overclocking. Pushing one's CPU past its default speed requires little more than turning up the multiplier. That can be done through increasingly user-friendly firmware interfaces and Windows software. Some boards will even overclock themselves—with and without your permission.
The obvious question, of course, is how Ivy Bridge fits into the overclocking picture. Intel's Sandy Bridge CPUs have offered a decent amount of clock speed headroom since their debut early last year, and all eyes are on Ivy to see if she can replicate that feat. To find out what the new platform has to offer overclockers, we've spend some quality time pushing the new Core i7-3770K on Z77 motherboards from Asus, Gigabyte, Intel, and MSI. Read on to see what we've learned.
Free as in headroom
There are all kinds of overclockers in the enthusiast community. Some spend ridiculous amounts of time—and money—on elaborate contraptions that chill CPUs using liquid nitrogen. Others plumb their PCs with intricate networks of water-cooling tubing. Those camps tend to seek out the absolute limits of their CPUs. However, most enthusiasts seem content to tap the "free" clock speed headroom that can be exploited with affordable air cooling. Rather than probing the extremes, we're going to see how far the Core i7-3770K goes with the sort of air tower one might expect to find inside the average enthusiast's PC.
After rummaging through the collection of heatsinks that has accumulated in the Benchmarking Sweatshop, we settled on a Thermaltake Frio. This is the same cooler we use on our storage test systems, and at $48 online, it's eminently affordable. The radiator is lined with more fins than we'd care to count, plus five heatpipes and dual 120-mm fans.
Where's the second spinner? It interfered with the taller heatspreaders on our Corsair Vengeance DIMMs, so the Frio had to make do with just a single fan for much of our testing. The clearance issue affected all four of the Z77 boards in our labs. We also had trouble getting a couple of larger Noctua coolers to fit, so the problem isn't unique to the Frio. Most motherboards put their DIMM slots too close to the socket to allow massive air coolers to coexist peacefully with taller memory modules.
As it turns out, the second fan didn't end up making much of a difference. When we switched to a dual-fan setup with a pair of low-profile Kingston DIMMs, we didn't notice a substantial decrease in CPU temperatures. The second fan didn't help the CPU hit higher speeds, either.
That's not to say that our overclocking endeavors weren't limited by our system's cooling setup. Although we managed to get up to 5GHz on a couple of the boards, the CPU temperature climbed high enough to boil water. Thermal throttling was rampant, forcing us to back off to 4.9GHz, the highest speed our Core i7-3770K would sustain under load.
To hit 4.9GHz, we used a 49X multiplier with Ivy's stock 100MHz base clock. It's also possible to increase the CPU frequency by turning up the base clock speed, but since that clock affects other system components, it's best to stick to multiplier tweaking. We were never able to squeeze more than a few MHz out of Sandy Bridge's base clock, and Intel says Ivy has a similar range.
Our Core i7-3770K needed 1.35V (which CPU-Z detected as 1.368V) to remain stable at 4.9GHz. The system was stressed with AIDA64's built-in torture test running alongside the rthdribl HDR lighting demo. That tandem made for a good quick test, but 7-Zip proved to be the final arbiter. When we ran it to gather final performance numbers for each motherboard, the app spit out errors with configurations that were previously thought to be stable.
I was a little surprised to hit obvious thermal limits with the chip running at such a relatively low core voltage. Then I looked at the power consumption. Here are some wattage numbers for the entire system, sans monitor, taken from the wall socket. A multi-core Cinebench render was used to generate the load.
Yeah, that's a pretty big difference under load. 4.4GHz represents the highest speed we achieved at the default voltage, which CPU-Z reported as 1.128V. That 500MHz jump over the Core i7-3770K's 3.9GHz peak Turbo frequency consumed an additional 17W at the wall socket. Going up another 400MHz with a voltage bump of 0.24V sent the reading on our watt meter up by nearly 100W.
Processor power consumption is proportional to the product of frequency and the square of the voltage, so increasing the latter can really cause the wattage to rise. We crunched the numbers, and our results fit the formula nicely. Serious cooling will be required to push Ivy to its limits. At the same time, taking Ivy up to around 4.4GHz should require only modest cooling, provided the CPU voltage is untouched.